This invention relates to a method of lining the interior walls of various installed pipes such as those for transmitting town gas, natural gas, petroleum, and water.
Typical examples of the conventional methods include the following:
(1) A method which involves insertion of a hard pipe such as a polyethylene pipe into a pipe to be treated.
(2) A method according to which a flexible tube of a film material provided in part with an adhesive agent is inserted into a pipe to be treated and then made to expand therein by applying or reducing pressure.
(3) A method according to which a liquid lining material is introduced into a pipe to be treated and then an object is passed through the pipe, making the lining material adhere to the pipe interior. Any superfluous amount of the lining material is recovered.
In the (1) method in which a pipe of a hard material is inserted into a pipe to be treated, the hard pipe must have a diameter considerably smaller than the internal diameter of the pipe to be treated, which results in a reduced sectional dimension of the fluid passage. This method has a further disadvantage in that it is applicable only to straight pipe portions and not to an installed pipe which generally has many bends. The (2) method makes only part of the film tube adhere to the interior wall of the pipe. In case a crack, for example, is present in the pipe, water may enter through the crack from outside and proceed between the tube and the pipe where no adhesion has occurred. This causes the tube to come off the interior wall of the pipe, reducing the effective fluid passage dimension and thus the transmitting capacity of the pipe. Furthermore, this method is liable to tearing of the tube when caught by rust on the interior wall of the pipe, or by bend portions or joint portions of the pipe. In the (3) method, the lining material may not be applied over the whole periphery and length of the pipe. The liquid lining material is likely to move down on the interior wall of the pipe before it cures, which results in an uneven layer of lining.
One solution to the above disadvantage may be the method disclosed in United Kingdom Pat. No. 1,039,836. This method comprises placing in a pipe a flexible liner tube together with a delivery hose for supplying an adhesive agent, retracting the hose from the pipe interior while supplying the adhesive agent into the pipe through an opening at an extreme end of the hose, and then passing an object through the liner tube to thereby cause the tube to adhere to the pipe interior. As the liner tube is of a flexible material, it is adaptable to any suitable shape for insertion into the pipe, and such tube may be readily inserted into a pipe with many bend portions. After insertion of the tube into the pipe, an object is passed through the tube to cause its adhesion to the pipe wall, and this has an advantage of good adhesion over the pressure applying or reducing method.
However, the method of this British patent is not without problems. Since the liner tube and the adhesive supplying hose are inserted into the pipe together, not only is the inserting operation difficult but the hose and the tube may get entangled with each other. The entanglement may cause them to be twisted or damaged. The same problem could occur when the hose is wound up from the pipe while supplying the adhesive agent into the pipe. Particularly when winding up the hose, the hose is likely to entangle with the tube or get caught by the interior wall of the pipe. This means an irregular withdrawal speed of the hose opening and an uneven supply of the adhesive agent along the pipe. Such a situation will bring about poor bonding of the tube onto the pipe. These defects of the method of the British patent will become more notable the longer or more curved the pipe is.
Even if supplied uniformly along the pipe, the adhesive agent lies only in the lower portion of the pipe interior, in other words at the lower forward face of the object to be passed. Therefore, the advancing object can hardly assure a positive distribution of the adhesive agent over the inner periphery of the pipe, which is likely to result in poor adhesion of the liner tube.
Moreover, the method of this British patent involves winding up of the hose when supplying the adhesive agent, which renders the whole operation complicated and time-comsuming.